Associated Topics || Dr. Math Home || Search Dr. Math

### What Are Variables For?

```
Date: 02/09/2001 at 04:54:54
From: Cindy
Subject: Variables

Hi!

I just wanted to ask, why is it important to be able to figure out the
values of variables? We've been doing that in our math class for
more than half a year and I was just wondering.

Cindy
```

```
Date: 02/09/2001 at 13:24:58
From: Doctor Ian
Subject: Re: Variables

Hi Cindy,

This is a very perceptive question.

Variables are important for a couple of reasons, which we might call
'planning' and 'analysis'.

Think about planning a dinner party. You know that you'll need one
half of a chicken for each adult, and one quarter of a chicken for
each child; you'll need one bottle of wine for every three adults, and
one bottle of soda for every five children; you'll need a half pound
of potatos for each chicken that you have to cook; you'll need one pie
for each six adults, and one bowl of jello for each child; and so on.

But you don't yet know how many people you're going to invite.
Variables let you set up a description of the situation (i.e., an
equation) such that you can plug in two numbers (the number of adults,
and the number of children) and get back other numbers that you'll
find useful: how many chickens to buy, how much the total cost will
be, and so on. If you decide at the last minute that you want to add
another three guests, you don't have to start your calculations from
scratch - you just change the values coming in, and the equations will
tell you how to change the values at the other end.

This, by the way, is why they are called 'variables' - they tell you
how some quantities vary in response to changes in other quantities.

Note that a dinner party isn't all that complicated, so it's almost
not worth the effort of setting up equations to solve the problems.
The same is true of a lot of the problems that you'd see in a math
class, which is one of the things that can make math (as it's taught
in schools) seem kind of pointless.

But when you get to something more complicated - like trying to plan a
flight, or run an entire airline - it becomes absolutely necessary to
make use of the kinds of techniques that you learn in your math
classes. A big part of running any business is being able to figure
out your potential costs in any situation, because that tells you how
much you need to charge for goods and services in order to make enough

So, that's planning. What about analysis? Well, analysis is just
planning in reverse. If you know how many people to invite, you can
figure out how much money you'll have to spend. That's planning. If
you know how much money you spent, you can figure out how many people
you invited. That's analysis. The beauty of variables is that in most
cases, you can use the same equations to go in either direction - to
predict what's going to happen, or to understand what already
happened.

The planning aspect tends to be more useful in things like business,
or construction, or engineering, where you have to decide what's going
to happen. The analysis aspect tends to be more useful in science,
where you don't get to decide what happens (the world behaves the way
it behaves, whether you like it or not), but would like to understand
it anyway, whether just from curiosity, or because you'd like to use
that understanding to make your planning more accurate.

more, or if you have any other questions.

- Doctor Ian, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics: